The present invention relates to a connection for two end portions of a conveyor belt or a power transmission belt of elastomeric material having a load-carrying member that is made of metal or woven material and is embedded between cover layers. The free ends of the load-carrying member are placed together in a connection location that is covered by a reinforcement that is embedded in elastomeric material and comprises a woven cover, or threads or wires that are oriented transverse or essentially transverse to the load-carrying members.
The task of the load-carrying member that is embedded in the conveyor belt or the power transmission belt is to transmit the forces that are introduced at the drive mechanisms. In a fabric-reinforced belt, the load-carrying means comprises one or more superimposed woven layers. Where the belt comprises steel cables, the load-carrying member is formed of steel cables or wires that are disposed in a plane, extend parallel to one another in the longitudinal direction of the belt, and are embedded in core rubber. In place of steel cables or wires, the load-carrying member can also comprise other filament-like strength carriers.
To close an open belt and make it continuous, and to join together several partial lengths, in most cases connections are established by vulcanization, whereby the belt tension forces are transmitted from one strength carrier to the other via shearing stresses in the rubber. The free ends of the load-carrying member are placed together in the connection location. In this connection, individual layers or cables of the load-carrying member can abut one another or can be disposed freely over or between the load-carrying member of the other belt end in an overlapping or intermeshing arrangement. In each case, the ends of the load-carrying member are freely embedded in the surrounding elastomeric material.
In the connection location, the tension forces of one load-carrying member are transmitted to the other load-carrying member through the rubber layers that are disposed therebetween. The forces are present in the form of a shearing stress.
With wire cable conveyor belts, the transfer of force from the cable of one belt end to the cable of the other belt end is effected via the rubber layer that is disposed therebetween and that must have at least a certain minimum thickness.
To transmit greater tension stresses, high strength conveyor belts are used, the connection location of which has a multi-stage configuration.
To protect the conveyor belt from damage or destruction, the conveyor belts are provided with an insert that is generally inserted between the band core and the upper and/or lower cover layer and that acts as a protection against cuts and penetrations. This insert is in the form of a reinforcing insert that comprises steel cables or similar filament-like structures, and that extends linearly and at an angle or transverse to the longitudinal direction of the conveyor belt and over the entire width of the belt, with the exception of narrow edge zones. This protective transverse reinforcement must also pass through the connection location of the conveyor belt.
It is also known to provide a transverse reinforcement just in the connection location of a belt that is otherwise not transversely reinforced. In so doing, the transverse reinforcement serves to increase the resistance to shearing in the connection location.
DE-PS 25 11 671 discloses a connection of the abutting end portions of a conveyor belt or power transmission belt that is made of rubber or rubber-like synthetic materials; in this connection, a transverse reinforcement is provided that comprises a reinforcement insert made up of spaced-apart parallel threads or wires that extend transverse or essentially transverse to the load-carrying member. In the central portion of the connection, the transversely disposed chord filaments have the narrowest spacing, which becomes increasingly greater in both directions toward the end regions. The entire length of the connection is covered with this transverse reinforcement.
To establish connections of steel cable conveyor belts, DIN (German industrial standard) 22129, section 4, prescribes that a transverse reinforcement in the carrying side should also be introduced in the region of the connection if the transverse reinforcement extends over the entire length of the conveyor belt. However, from the transition zones, in which the covers are inclined relative to the core of the belt, a small gap of approximately 50mm must be maintained for the convenience of the worker.
Obviously, the weakest spot of a conveyor belt is its connection. The fatigue strength of the belt is limited by the dynamic durability of the connection.
It has been discovered that the disintegration of the connection begins at the free ends of the two load-carrying member ends. With a wire cable conveyor belt, this disintegration can result in a working-out of the ends of the wire cables. Thus, the elastomeric material at the free ends of the load-carrying member proves to be the weakest point of the connection, even if the force that is to be transmitted at that location is very small in comparison to the individual tension stresses in the load-carrying member. This is attributed to the fact that at the free ends in the elastomeric material shearing stresses result that are proportional to the tension stresses. The high shearing stress of the elastomeric material at the free ends is the cause for the start of a possible belt disintegration at that location.
In order to reduce the shearing in the connection and to increase the dynamic strength, it is known to increase the gaps between the load-carrying members via special arrangement patterns. Transverse reinforcements also contribute to the reduction because they increase the resistance to shearing. However, there is still a requirement for a further increase of the dynamic strength of the connection.
It is therefore an object of the present invention to increase the dynamic strength of the connection of conveyor belts or power transmission belts.